\Sly\, a. [Compar. {Slier}or {Slyer}; superl. {Sliest} or
{Slyest}.] [OE. sli, slegh, sleih, Icel sl?gr, for sl?gr;
akin to Sw. slug, Dan. slu, LG. slou, G. schlau; probably to
E. slay, v.t.; cf. G. verschlagen sly. See {Slay}, v. t., and
cf. {Sleight}.]
1. Dexterous in performing an action, so as to escape notice;
   nimble; skillful; cautious; shrewd; knowing; -- in a good
   sense.
         Be ye sly as serpents, and simple as doves. --Wyclif
                                               (Matt. x. 16).
         Whom graver age And long experience hath made wise
         and sly.                              --Fairfax.
2. Artfully cunning; secretly mischievous; wily.
         For my sly wiles and subtle craftiness, The litle of
         the kingdom I possess.                --Spenser.
3. Done with, and marked by, artful and dexterous secrecy;
   subtle; as, a sly trick.
         Envy works in a sly and imperceptible manner. --I.
                                               Watts.
4. Light or delicate; slight; thin. [Obs.]
{By the sly}, or {On the sly}, in a sly or secret manner.
   [Colloq.] ``Gazed on Hetty's charms by the sly.'' --G.
   Eliot.
{Sly goose} (Zo["o]l.), the common sheldrake; -- so named
   from its craftiness.
Syn: Cunning; crafty; subtile; wily. See {Cunning}.

\Sly\, adv.
Slyly. [Obs. or Poetic] --Spenser.